The literature specifies highly varying methods for the construction of three-dimensional objects of “light—hardening” photopolymers, cf. “Automated Fabrication—Improving Productivity in Manufacturing” by Marshall Burns, 1993 (ISBN 0-13-119462-3).
Known possibilities are, inter alia, the exposure by    a) multimedia projector    b) LC display (reflexive, transmissive)    c) LED or laser diode line (which is moved over an area orthogonally to the line)    d) light valve technology (MEMS).
These methods are described in the following patents:
US Patent US005247180A “Stereolithographic Apparatus and Method of use” by Texas Instruments Inc., September 1993;
US Patent US005980813A “Rapid Prototyping using multiple materials” by SRI International, November 1999;
Utility model publication DE G 93 19 405.6 “Device for the production of a three-dimensional object (model) according to the principle of photo solidification” by the Research Center Informatics at the University of Karlsruhe, December 1993;
According to a similar method, the utility model publication DE 299 11 122 U1 “Device for producing a three-dimensional object”, DeltaMed inter alia, June 1999 describes an application for the generation of micro-technical, three-dimensional components.
EP 1250997A (=US2002155189A) “Device for producing a three-dimensional object” by Envision Technologies GmbH, April 2002.
German Patent DE69909136T “Rapid Prototyping Device and Rapid Prototyping Method”, July 2003 (equivalent: European Patent EP 1156922 “Rapid Prototyping Apparatus and Method of Rapid Prototyping”, August 2003) of DICON AS Lystrup, Denmark.
WO 01/00390 A by HAP, Sitec Industrietechnologie and DELTAMED Medizinprodukte GmbH.
WO 2005/110722 A of Envisiontec GmbH.
With laser-based systems for photo-polymerization, the light output in the exposure point is provided by the energy setting of the laser beam, whereby the hardening depth of the photopolymer can be controlled in that point. To selectively harden a corresponding layer, the laser beam is scanned over the cross-sectional surface to be correspondingly hardened.
The contours of the cross-sectional surface to be hardened can be scanned by the laser beam as a curve.
With systems for photo-polymerization based on mask projection by means of projection systems with the SLM technology, the advantage is that an entire cross-sectional area can be exposed at once. The light areas of the projected raster image harden the photopolymer voxel by voxel.
The disadvantage in projection systems with SLM technology is that the light output distribution over the image surface can be very inhomogeneous (up to 50% absolute), depending on                a) the light source used;        b) the optical system for coupling the light energy to the SLM; and        c) by the vignetting of the projection optics.        
The change of the properties of the light source over the service life will result in a variable error and thus in a changing homogeneity distribution.
Moreover, a change of the light intensity of the light source does not result in a selective change as with a laser but would affect the entire projection image.
A constant error is concerned in case of homogeneity deviations caused by the optical system for coupling the light energy to the SLM and the projection optics.
The contours of the cross-sectional surface to be hardened can only be presented in rasters; the resolution depends on the number of image points/pixels and on the size of the projected image.
Moreover, the light intensity varies depending on the size of the exposed surface structure (higher light intensity with larger, contiguous surfaces; lower light intensity with smaller, filigree surface structures).
With the above mentioned WO 01/00390 A, the intensity of beams is controlled by controlling the permeability of the mask, wherein the intensity may be controlled via the selection of gray levels of a transmission LCD.
In WO 2005/110722 A, a multiple exposure is carried out on the subpixel level per layer for improving the resolution along the outside and inside contours of the cross-sectional areas of the object to be generated, said exposure consisting of a sequence of a plurality of images offset on the subpixel level in the image/building plane, wherein a separate mask/bitmap is generated for every offset image.
Neither WO 01/00390 A nor WO 2005/110722 show how the resolution and the fine adjustment in the image plane can be improved and how native inhomogeneities of the light source can be balanced better.